Liquid crystal display device

ABSTRACT

In one embodiment, a liquid crystal display device includes a first substrate and a second substrate. The first substrate includes a first source line and a second source line extending in a first direction, a main pixel electrode arranged between the first source line and a second source line and extending in the first direction, and a pair of first main common electrodes arranged on the first source line and the second source line interposing an insulating layer and extending in the first direction, respectively. The second substrate includes a pair of second main common electrode arranged above the first main common electrode and extending in the first direction, and the first main common electrode is connected with the second main common electrode. A liquid crystal layer is held between the first substrate and the second substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2011-078553, filed Mar. 31, 2011,the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a liquid crystaldisplay device.

BACKGROUND

In recent years, a flat panel display device is developed briskly, andespecially the liquid crystal display device gets a lot of attentionfrom advantages, such as light weight, thin shape, and low powerconsumption. Especially, in an active matrix type liquid crystal displaydevice equipped with a switching element in each pixel, a structureusing lateral electric field, such as IPS (In-Plane Switching) mode andFFS (Fringe Field Switching) mode, attracts attention. The liquidcrystal display device using the lateral electric field mode is equippedwith pixel electrodes and common electrodes formed in an arraysubstrate, respectively. Liquid crystal molecules are switched by thelateral electric field substantially in parallel with the principalsurface of the array substrate.

On the other hand, another technique is also proposed, in which theliquid crystal molecules are switched using the lateral electric fieldor an oblique electric field between the pixel electrode formed in thearray substrate and the common electrode formed in a counter substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute aportion of the specification, illustrate embodiments of the invention,and together with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a figure schematically showing a structure of a liquid crystaldisplay device according to this embodiment.

FIG. 2 is a figure schematically showing the structure and theequivalent circuit of a liquid crystal display panel shown in FIG. 1.

FIG. 3 is a plan view schematically showing a minimum unit constituentof one pixel.

FIG. 4 is a cross-sectional view schematically showing the liquidcrystal display panel including a switching element, etc.

FIG. 5 is a plan view schematically showing a structure of one pixel ina counter substrate according to this embodiment.

FIG. 6 is a plan view schematically showing a structure of an arraysubstrate of the pixel in the liquid crystal display panel when thepixel is seen from the counter substrate side according to thisembodiment.

FIG. 7 is a cross-sectional view schematically showing the structure ofthe pixel taken along line A-A shown in FIG. 6. FIG. 8A and FIG. 8B arefigures showing definition of a cross-talk rate introduced in thisembodiment.

DETAILED DESCRIPTION

A liquid crystal display device according to an exemplary embodiment ofthe present invention will now be described with reference to theaccompanying drawings wherein the same or like reference numeralsdesignate the same or corresponding portions throughout the severalviews.

According to one embodiment a liquid crystal display device, includes: afirst substrate including a first source line and a second source lineextending in a first direction, a main pixel electrode arranged betweenthe first source line and the second source line and extending in thefirst direction, and a pair of first main common electrodes arranged onthe first source line and the second source line interposing aninsulating layer and extending in the first direction, respectively; asecond substrate including a pair of second main common electrodesarranged above the first main common electrode and extending in thefirst direction, the first main common electrode being connected withthe second main common electrode; and a liquid crystal layer heldbetween the first substrate and the second substrate.

FIG. 1 is a figure schematically showing the structure of the liquidcrystal display device according to one embodiment.

The liquid crystal display device 1 includes an active-matrix typeliquid crystal display panel LPN, a driver IC chip 2 connected to theliquid crystal display panel LPN, a flexible wiring substrate 3, abacklight 4 for illuminating the liquid crystal display panel LPN, etc.

The liquid crystal display panel LPN is equipped with an array substrateAR as a first substrate, a counter substrates CT as a second substratearranged opposing the array substrate AR, and a liquid crystal layer(not shown) held between the array substrate AR and the countersubstrates CT. The liquid crystal display panel LPN includes an activearea ACT which displays images. The active area ACT is constituted by aplurality of pixels PX arranged in the shape of a (m×n) matrix (here,“m” and “n” are positive integers).

The backlight 4 is arranged on the back side of the array substrate ARin the illustrated example. Various types of backlights can be used asthe backlight 4. For example, a light emitting diode (LED) or a coldcathode fluorescent lamp (CCFL), etc., can be applied as a light sourceof the backlight 4, and the explanation about its detailed structure isomitted.

FIG. 2 is a figure schematically showing the structure and theequivalent circuit of the liquid crystal display panel LPN shown in FIG.1.

The liquid crystal display panel LPN is equipped with “n” gate lines G(G1-Gn), “n” auxiliary capacitance lines C (C1-Cn), “m” source lines S(S1-Sm), etc., in the active area ACT. The gate line G and the auxiliarycapacitance line C are respectively arranged along a first direction Yby turns. Moreover, the gate line G and the auxiliary capacitance line Cextend in parallel each other in a second direction X that intersectsperpendicularly the first direction Y. However they do not necessarilyextend linearly. The source lines S extend in the first direction Y thatintersects the gate line G and the auxiliary capacitance line C inparallel. Though the source lines S extend in the first direction Y,respectively, they do not necessarily extend linearly. The gate line G,the auxiliary capacitance line C and source lines S may be crookedpartially.

Each gate line G is pulled out to the outside of the active area ACT,and is connected to a gate driver GD. Each source line S is pulled outto the outside of the active area ACT, and is connected to a sourcedriver SD. At least a portion of the gate driver GD and the sourcedriver SD is formed in the array substrate AR, for example, and the gatedriver GD and the source driver SD are connected with the driver IC chip2 provided in the array substrate AR and having an implementedcontroller.

Each pixel PX includes a switching element SW, a pixel electrode PE, acommon electrode CE, etc. Retention capacitance Cs is formed, forexample between the auxiliary capacitance line C and the pixel electrodePE.

In addition, in the liquid crystal display panel LPN according to thisembodiment, while the pixel electrode PE is formed in the arraysubstrate AR, the common electrode CE is formed in the array substrateAR and the counter substrate CT. The liquid crystal molecule of a liquidcrystal layer LQ is switched mainly using an electric field formedbetween the pixel electrodes PE and the common electrodes CE. Theelectric field formed between the pixel electrode PE and the commonelectrode CE is a lateral electric field substantially in parallel withthe principal surface of the array substrate AR or the principal surfaceof the counter substrate CT, or an oblique electric field slightlyoblique with respect to the principle surface of the substrates.

The switching element SW is constituted by n channel type thin filmtransistor (Tyr), for example. The switching element SW is electricallyconnected with the gate line G and the source line S. The (m×n)switching elements SW are formed in the active area ACT.

The pixel electrode PE is electrically connected with the switchingelement SW. The (m×n) pixel electrodes PE are formed in the active areaACT. The common electrode CE is set to a common potential, for example.The common electrode CE is arranged in common to the plurality of pixelelectrodes PE through the liquid crystal layer LQ. The common electrodeCE is electrically connected with an electric power supply portion VSformed in the array substrate AR through an electric conductivecomponent which is not illustrated. The auxiliary capacitance line C iselectrically connected with a voltage impressing portion VCS to whichthe auxiliary capacitance voltage is impressed.

The array substrate AR includes an electric power supply portion VSformed outside of the active area ACT. A portion of the common electrodeCE formed on the array substrate AR is connected with the electric powersupply portion VS at the outside of the active area ACT. Furthermore, aportion of the common electrode CE formed on the counter substrate CT iselectrically connected with the electric power supply portion VS formedin the array substrate AR through an electric conductive component whichis not illustrated.

FIG. 3 is a plan view schematically showing a minimum unit constituentof one pixel PX.

The pixel electrode PE has a main pixel electrode PA and a capacitanceportion PC. The main pixel electrode PA and the capacitance portion PCare electrically connected each other. All the pixel electrodes PE areformed on the array substrate AR in this embodiment.

The main pixel electrode PA extends along the first direction Y. Thecapacitance portion PC extends along the second direction X differentfrom the first direction Y. More specifically, the main pixel electrodePA is formed in the shape of a belt linearly extending along the firstdirection Y approximately in the central portion of the pixel. Thecapacitance portion PC is formed in the shape of a belt linearlyextending along the second direction X in an upper end portion of thepixel PX. In addition, the capacitance portion PC may be arrangedbetween up-and-down adjacent pixels PX. That is, the capacitance portionPC may be arranged striding over a boundary between the illustratedpixel PX and the adjacent pixel PX (not shown) of the upper portion.

The capacitance portion PC is connected with one end of the main pixelelectrode PA and extends toward its both sides from the main pixelelectrode PA. The capacitance portion PC is orthogonally crosses themain pixel electrode PA. In addition, the capacitance portion PC may bearranged on the other end portion side rather than one end portion ofthe main pixel electrode PA. The pixel electrode PE is electricallyconnected with the switching element (not shown) in this capacitanceportion PC, for example.

The common electrode CE includes a plurality of main common electrodesCA. The main common electrodes CA are electrically connected each other.The common electrode CE is insulated electrically from the pixelelectrode PE. In this embodiment, at least some portions of the maincommon electrode CA in the common electrode CE are formed on the countersubstrate CT.

The main common electrode CA extends along the first direction Y. In theillustrated example, the main common electrode CA is formed in the shapeof a belt linearly extending along the first direction Y. In addition,the main common electrode CA is arranged in two parallel lines.Hereinafter, in order to distinguish the two main common electrodes CArespectively, the main common electrode of the left-hand side in thefigure is called CAL, and the main common electrode of the right-handside in the figure is called CAR.

The main common electrode CAL and the main common electrode CAR arearranged between adjacent right-and-left pixels. That is, the maincommon electrode CAL is arranged striding over a boundary between theillustrated pixel PX and the pixel (not shown) of the left-hand side,and the main common electrode CAR is arranged striding over a boundarybetween the illustrated pixel PX and the pixel (not shown) of theright-hand side.

The pair of main common electrode CA is arranged so as to sandwich themain electrode PA. That is, the main common electrode CA and the mainpixel electrode PA are arranged by turns along the second direction X.The main pixel electrode PA and the pair of main common electrode CA arearranged approximately in parallel each other. At this time, in a X-Yplane, none of the main common electrodes CA overlaps the main pixelelectrode PA in the X-Y plane, but an aperture which contributes mainlyto the display is formed between each of the main common electrode CAand the main pixel electrodes PA.

That is, one main pixel electrode PA is located between the adjoiningmain common electrode CAL and main common electrode CAR. In other word,the main common electrode CAL and the main common electrode CAR arearranged at the both sides which sandwich the main pixel electrode PA.For this reason, the main common electrode CAL, the main pixel electrodePA, and the main common electrode CAR are arranged along the seconddirection X in this order.

The distance between the main common electrode CAR and the main pixelelectrode PA is substantially the same as that between the main commonelectrode CAL and the main pixel electrode PA in the second direction X.Apertures are formed between the main common electrode CAL and the mainpixel electrode PA, and between the main pixel electrode PA and the maincommon electrode CAR, respectively. That is, in the example shown here,two apertures are formed in one PX.

In this embodiment, the initial alignment direction of the liquidcrystal molecule LM is substantially in parallel with the firstdirection Y, however, may be an oblique direction D crossing the firstdirection Y. Here, the angle θ1 between the first direction Y and theinitial alignment direction D is set to an angle larger than 0° andsmaller than 45°. From a viewpoint of alignment control of the liquidcrystal molecules, it is extremely effective that the angle θ1 is set toapproximately 5° to 25°, and more preferably, around 10°. Here, theangle θ1 is a slightly oblique direction by about several degrees, forexample, 7°, with respect to the first direction Y.

In addition, the pixel electrode PE may be further equipped withsub-pixel electrodes which extend along the second direction X.Moreover, the common electrode CE may be further equipped withsub-common electrodes which extend along the second direction X.

FIG. 4 is a view schematically showing the cross-section of the liquidcrystal display panel LPN including the switching element SW, the gateline G, and the auxiliary capacitance line C. In addition, illustrationof the common electrode is omitted and only the portion required forexplanation is illustrated here.

The backlight 4 is arranged at the back side of the array substrate ARwhich constitutes the liquid crystal display panel LPN.

The array substrate AR is formed using an insulating substrate 10 havinga light transmissive characteristic, such as a glass substrate and aplastic substrate. This array substrate AR includes the switchingelement SW, the pixel electrode PE, the first alignment layer AL1, etc.,on the first insulating substrate 10 on the side facing the countersubstrate CT.

In the example shown here, the switching element SW may be either a topgate-type switching element or a bottom gate-type switching element, andincludes a semiconductor layer formed of a poly-silicon or amorphoussilicon, though the detailed description thereof is not made.

The semiconductor layer SC has a source region SCS and a drain regionSCD on both sides which faces across a channel region SCC, respectively.In addition, an undercoat layer which is an insulating film may bearranged between the first insulating substrate 10 and the semiconductorlayer SC. The semiconductor layer SC is covered with a gate insulatingfilm 11. Moreover, the gate insulating film 11 is arranged also on thefirst insulating substrate 10.

The gate electrode WG is formed on the gate insulating film 11, and islocated on the channel region SCC of the semiconductor layer SC. Thegate line G and the auxiliary capacitance line C are also formed on thegate insulating film 11. The gate electrode WG, gate line G and theauxiliary capacitance line C may be formed using the same process andthe same material. The gate electrode WG is electrically connected withthe gate line G.

The gate electrode WG and the auxiliary capacitance line C are coveredwith a first interlayer insulating film 12. Moreover, the firstinterlayer insulating film 12 is arranged also on the gate insulatingfilm 11. The gate insulating layer and 11 and the first interlayerinsulating film 12 are formed of an inorganic system material, such assilicon oxide and a silicon nitride.

A source electrode WS and a drain electrode WD of the switching elementSW are formed on the first interlayer insulating film 12. The sourceline (not shown) is also formed on the first interlayer insulating film12. Moreover, in this figure, the source line S (not shown) formed onthe first interlayer insulating film 12 is also illustrated. The sourceelectrode WS, the drain electrode WD, and the source lines S1 and S2 maybe formed using the same process and the same material. The sourceelectrode WS is electrically connected with the source lines.

The source electrode WS is in contact with the source region SCS of thesemiconductor layer SC through a contact hole which penetrates the gateinsulating film 11 and the first interlayer insulating film 12. Thedrain electrode WD is in contact with the drain region SCD of thesemiconductor layer SC through a contact hole which penetrates the gateinsulating film 11 and the first interlayer insulating film 12. The gateelectrodes WG, the gate line G, the auxiliary capacitance line C, thesource electrode WS, the drain electrode WD, and the source line areformed of electric conductive materials, such as molybdenum, aluminum,tungsten, and titanium, for example.

The switching element SW as described-above is covered with a secondinterlayer insulating film 13. That is, the source electrode WS, thedrain electrode WD, and the source lines are covered with the secondinterlayer insulating film 13. Moreover, the second interlayerinsulating film 13 is arranged also on the first interlayer insulatingfilm 12. This second interlayer insulating film 13 is formed of variousorganic materials, such as ultraviolet curing type resin and heat curingtype resin, for example.

The pixel electrode PE is formed on the second interlayer insulatingfilm 13. Though not described in detail, the main pixel electrode PA andthe capacitance portion PC forming the pixel electrode PE are formed onthe second interlayer insulating film 13. The pixel electrode PE isconnected with the drain electrode WD through a contact hole whichpenetrates the second interlayer insulating film 13. Though pixelelectrode PE is formed by light transmissive conductive materials, suchas Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), etc, other metalssuch as aluminum may be used.

In addition, the array substrate AR is further equipped with a firstmain common electrode as a portion of the common electrode to bementioned later.

A first alignment film AL1 is arranged on a surface of the arraysubstrate AR facing the counter substrate CT, and extends approximatelywhole region of the active area ACT. The first alignment film AL1 coversthe pixel electrode PE and the first main common electrode (not shown),and also formed on the second interlayer insulating film 13. The firstalignment film AL1 is formed of the material which shows a lateralalignment characteristics.

On the other hand, the counter substrate CT is formed using a secondtransmissive insulating substrate 20, such as a glass substrate and aplastic substrate. The counter substrate CT includes a second maincommon electrode of the common electrode (not shown) and a secondalignment film AL2 on the surface of the second insulating substrate 20facing the array substrate AR. A black matrix arranged facing wiringportions such as the source line S, the gate line G, the auxiliarycapacitance line C, and the switching element SW to define therespective pixels PX, color filter layers arranged corresponding to thepixels PX, and an overcoat layer to smooth the concave and depression ofthe surface of the black matrix and the color filter layer may be formedon the counter substrate CT.

The common electrode is formed of the electric conductive material whichhas light transmissive characteristics, such as ITO and IZO, forexample.

The second alignment films AL2 is arranged on the surface of the countersubstrate CT opposing the surface of the array substrate AR, and extendsapproximately whole of the active area ACT. The second alignment filmsAL2 covers the second main common electrode of the common electrode (notshown) and the like. The second alignment films AL2 is formed materialswhich has a lateral alignment characteristics

In the first and second alignment films AL1 and AL2, alignment treatmentprocessing (for example, rubbing processing and photo alignmentprocessing) is performed for making the liquid crystal display moleculein an initial alignment state. The first alignment treatment directionin which the first alignment film AL1 makes the liquid crystal moleculein the initial alignment direction, the second alignment treatmentdirection in which the second alignment film AL2 makes the liquidcrystal molecule in the initial alignment direction, are respectivelydirections in parallel to the first direction Y or an slightly obliquedirection D crossing the first direction Y. The first and secondalignment treatment directions are in parallel each other, and in thesame or reverse direction.

The array substrate AR and the counter substrate CT as mentioned-aboveare arranged so that the first alignment film AL1 and the secondalignment film AL2 face each other. In this case, the pillar-shapedspacer is formed integrally with one of the substrates by resin materialbetween the first alignment film AL1 on the array substrate AR and thesecond alignment film AL2 on the counter substrate CT. Thereby, apredetermined gap, for example, a 3-7 μm cell gap, is formed, forexample. The array substrate AR and the counter substrate CT are pastedtogether by seal material which is not illustrated, in which thepredetermined cell gap is formed.

The liquid crystal layer LQ is held at the cell gap formed between thearray substrate AR and the counter substrate CT, and is arranged betweenthe first alignment film AL1 and the second alignment film AL2. Theliquid crystal layer LQ contains the liquid crystal molecule which isnot illustrated. The liquid crystal layer LQ is constituted by positivetype liquid crystal material.

A first optical element OD1 is attached to the external surface of thearray substrate AR, i.e., the external surface of the first insulatingsubstrate 10 which constitutes the array substrate AR by adhesives, etc.The first optical element OD1 contains first polarizing plate PL1 whichhas a first polarization axis. Moreover, a second optical element OD2 isattached to the external surface of the counter substrate CT, i.e., theexternal surface of the second insulating substrate 20 which constitutesthe counter substrate CT by adhesives, etc. The second optical elementOD2 contains a second polarizing plate PL2 which has a secondpolarization axis. The first polarization axis of the first polarizingplate PL1 and the second polarization axis of the second polarizingplate PL2 are in the spatial relationship in which both of the first andsecond polarizing plate PL1 and PL2 intersect perpendicularly, forexample. One polarizing plate is arranged, for example, so that itspolarizing direction is the direction of the long axis of the liquidcrystal molecule, i.e., the first alignment treatment direction or aparallel direction to the second alignment treatment direction (or inparallel to the first direction Y), or in an orthogonal direction (or inparallel to the second direction X). Thereby, the normally black mode isachieved.

Namely, at the time of non-electric field state, i.e., when a potentialdifference (i.e., electric field) is not formed between the pixelelectrode PE and the common electrode CE, the liquid crystal moleculesLM of the liquid crystal layer LQ are aligned so that their long axisare aligned in a parallel direction with the first alignment directionof the first alignment film AL1 and the second alignment direction ofthe second alignment film AL2 as shown with a dashed line in FIG. 3. Inthis state, at the time of OFF, the alignment state corresponds to theinitial alignment state, and the alignment direction of the liquidcrystal molecule LM corresponds to the initial alignment direction.

In addition, precisely, the liquid crystal molecules LM are notexclusively aligned in parallel with a X-Y plane, but are pre-tilted inmany cases. For this reason, the precise direction of the initialalignment is a direction in which an orthogonal projection of thealignment direction of the liquid crystal molecule LM at the time of OFFis carried out to the X-Y plane. However, in order to explain simplyhereinafter, the liquid crystal molecule LM is assumed that the liquidcrystal molecule LM is aligned in parallel with a X-Y plane, and isexplained as what rotates in a field in parallel with the X-Y plane.

Here, both of the first alignment treatment direction of the firstalignment film AL1 and the second alignment treatment direction of thesecond alignment film AL2 are directions in parallel to the firstdirection Y or directions in parallel to the oblique direction D. At thetime of OFF, the long axis of the liquid crystal molecule LM is alignedsubstantially in parallel to the first direction Y or the obliquedirection D. That is, the direction for initial alignment of the liquidcrystal molecule LM is in parallel to the first direction Y or theoblique direction D. In the example shown in FIG. 3, the initialalignment direction of the liquid crystal molecule LM is in parallel tothe first direction Y.

In addition, when both of the first and second alignment treatmentdirections are in parallel, and are reverse directions each other, theliquid crystal molecule LM is aligned so that the liquid crystalmolecule LM is aligned with an approximately uniform pre-tilt angle nearthe first and second alignment films AL1 and AL2 and in the intermediateportion of the liquid crystal layer LQ (homogeneous alignment). Inaddition, when the respective directions of the alignment treatment ofthe first alignment film AL1 and the second alignment film AL2 are inparallel and the same each other, the liquid crystal molecule LM isaligned with approximately horizontal direction (i.e., the pre tiltangle is approximately zero) in a cross-section of the liquid crystallayer LQ. The liquid crystal molecule LM is aligned with the pre-tiltangle so that the alignment of the liquid crystal molecule LM near thefirst alignment film AL1 and the second alignment film AL2 becomessymmetrical with respect to the intermediate area of the liquid crystallayer LQ (splay alignment).

Some of the back light from the backlight 4 enters into the liquidcrystal display panel LPN after penetrating the first polarizing platePL1. The polarization state of the light which enters into the liquidcrystal display panel LPN changes depending on the alignment state ofthe liquid crystal molecule LM when the light passes the liquid crystallayer LQ. At the time of OFF, the light which passes the liquid crystallayer LQ is absorbed by the second polarizing plate PL2 (black display).

On the other hand, in case where the potential difference is formedbetween the pixel electrode PE and the common electrode CE (at the timeof ON), the lateral electric field in parallel to the substrate (oroblique electric field) is formed between the pixel electrode PE and thecommon electrode CE Thereby, the liquid crystal molecule LM rotateswithin a parallel plane with the substrate surface so that the long axisbecomes in parallel with the direction of the electric field as shown ina dashed line in FIG. 3.

In the example shown in FIG. 3 the liquid crystal molecule LM betweenthe main pixel electrode PA and main common electrode CAL rotatescounterclockwise along with the lateral electric field between the mainelectrode PA and the main common electrode CAL, and is aligned so thatthe liquid crystal molecule LM may turn to the upper left direction inthe figure. The liquid crystal molecule LM between the main electrode PAand the common main electrode CAR rotates clockwise along with thelateral electric field between the main electrode PA and the common mainelectrode CAR, and is aligned so that the liquid crystal molecule LM mayturn to the upper right direction in the figure.

Thus, in each pixel PX, where horizontal electric field is formedbetween the pixel electrode PE and the common electrode CE, thealignment direction of the liquid crystal molecule LM is divided into atleast two groups of directions, and two domains are formed correspondingrespective alignment directions. That is, at least two domains areformed in each pixel PX.

At the time of ON, the light which entered into the liquid crystal panelLPN from the backlight 4 enters into the liquid crystal layer LQ. Whenthe back light which entered into the liquid crystal layer LQ passesthrough two domains (apertures) divided with the pixel electrode PE andthe common electrode CE, respectively, the polarization state changes.At the time of ON, at least a portion of light which passed the liquidcrystal layer LQ penetrates the second polarizing plate PL2 (whitedisplay).

According to this embodiment, it becomes possible to form at least twodomains. Therefore, the viewing angle in at least two directions can becompensated optically, and a wide viewing angle is attained whilebecoming possible to suppress the generation of gradation reversal.Accordingly, it becomes possible to offer a high quality display device.

Moreover, the transmissivity of each domain becomes equal by setting upthe area of at least two apertures divided with the pixel electrode PEand the common electrode CE substantially equal in one pixel. Therefore,it becomes possible to achieve a uniform display with wide viewing angleby compensating the light passing the respective apertures opticallyeach other.

Furthermore, at the time of ON, since the horizontal electric field ishardly formed (or sufficient electric field to drive the liquid crystalmolecule LM is not formed) near the main pixel electrode PA of the pixelelectrode PE, the liquid crystal molecule LM hardly moves from theinitial alignment direction like at the time of OFF. For this reason, asmentioned-above, even if the pixel electrode PE and the common electrodeCE are formed of the electric conductive material with the lighttransmissive characteristics in these domains, back light hardlypenetrates, i.e., hardly contributes to the display at the time of ON.Therefore, the pixel electrode PE and the common electrode CE do notnecessarily need to be formed of a transparent electric conductivematerial, and may be formed using electric conductive materials, such asaluminum and silver.

Moreover, when an alignment shift occurs between the array substrate ARand the counter substrate CT, a difference may arises in distancebetween the respective common electrodes CE of the both sides and thepixel electrode PE. However, since the alignment shift is produced incommon to all the pixels PX, there is no difference in the electricfield distribution between the pixels PX, and the influence to thedisplay of the image is negligible.

Next, one example of the structure according to this embodiment isexplained. FIG. 5 is a plan view schematically showing the structure ofone pixel in the counter substrate CT of the liquid crystal panel LPN.

In the example of the structure explained here, the common electrode CEhas a first main common electrode in the array substrate which is notillustrated, and second main common electrode CA2 formed in the countersubstrate CT.

The illustrated counter substrate CT includes a second main commonelectrode CA2 in a belt shape extending linearly along the firstdirection Y. A plurarity of second main common electrodes CA2 iselectrically connected each other. In the illustrated example, thecommon electrode CE is formed in the shape of a stripe in the countersubstrate CT.

In addition, the second main common electrodes CA2 illustrated areformed in two parallel lines along the second direction X. Hereinafter,in order to distinguish these common electrodes, the second main commonelectrode of the left-hand side in a figure is called CAL2, and thesecond main common electrode of the right-hand side in a figure iscalled CAR2. Although such second main common electrode CA2 of thecommon electrode CE is not explained in detail, the second main commonelectrode CA2 is pulled out to the outside of the active area, and iselectrically connected with the electric supply portion formed in thearray substrate through an electric conductive component, and electriccommon potential is supplied.

Next, the array substrate AR which is suitably combined with the countersubstrate CT shown in FIG. 5 is explained.

FIG. 6 is a plan view schematically showing the structure of the arraysubstrate AR when one pixel PX of the liquid crystal panel LPN in theexample of one structure according to this embodiment is seen from thecounter substrate CT side. In addition, only structure required for theexplanation in one PX is illustrated, and illustration of the switchingelement, etc., is omitted.

The array substrate AR includes an auxiliary capacitance line C1 and anauxiliary capacitance line C2 extending along the second direction X, agate line G1 extending along the second direction X, a source line S1and the source line S2 extending along the first direction Y, a pixelelectrode PE, and a belt-like first main common electrode CA1 extendinglinearly along the first direction Y as the common electrodes CE. Theauxiliary capacitance line C1, the auxiliary capacitance line C2, andthe gate line G1 are formed on the gate insulating film 11, and arecovered with the first interlayer insulating film 12. The source line S1and the source line S2 are formed on the first interlayer insulatingfilm 12, and are covered with the second interlayer insulating film 13.The pixel electrode PE is formed on the second interlayer insulatingfilm 13. The first main common electrode CA1 is formed on the secondinterlayer insulating film 13, for example, like the pixel electrode PE.

In the illustrated example, the pixel PX corresponds to a region shownin dashed line in the figure, and has the shape of a rectangle in whichthe length in the first direction Y is longer than that in the seconddirection X. Moreover, in the illustrated example, the source line S1 isarranged at the left-hand side end in the pixel PX. Precisely, thesource line S1 is arranged striding over the boundary between theillustrated pixel and the pixel which adjoins the illustrated pixel PXat its left-hand side end. The source line S2 is arranged at theright-hand side end. Precisely, the source line S1 is also arrangedstriding over the boundary between the illustrated and the pixel whichadjoins the illustrated pixel PX at its right-hand side end. Theauxiliary capacitance line C1 is arranged at the upper portion end. Inaddition, the gate line G1 is arranged approximately in the centralportion of the pixel PX. The auxiliary capacitance line C1 may bearranged striding over the boundary between the illustrated pixel PX andthe adjacent pixel PX of the upper side. Similarly, the auxiliarycapacitance line C2 may be arranged striding over the boundary betweenthe illustrated pixel PX and the adjacent pixel of the bottom side.

In the common electrode CE, the first main common electrode CA1illustrated is formed in parallel two lines along the second directionX. Hereinafter, in order to distinguish the main common electrodes, thefirst main common electrode of the left-hand side in the figure iscalled CAL1, and the first main common electrode of the right-hand sidein the figure is called CAR1. When the first main common electrode CA1is formed on the second interlayer insulating film 13 with the pixelelectrode PE, the first main common electrode CA1 can be formed usingthe same process and the same materials (for example, ITO, etc.,) as thepixel electrode PE.

In addition, other interlayer insulating films may be arranged betweenthe first main common electrode CA1 and the pixel electrode PE, and thefirst main common electrode CA1 may be formed of a different layer fromthe pixel electrode PE. In this case, the first main common electrodeCA1 may be formed of material which is different from the pixelelectrode PE, or may be formed of the same material as the pixelelectrode PE.

In the illustrated example, the first main common electrode CAL1 isarranged at the left-hand side end of the pixel PX, and faces the sourceline S1. Moreover, the first main common electrode CAR1 is arranged atthe right-hand side end of the pixel PX, and faces the source line S2.

The first main common electrodes CA1 linearly extending in each activearea are pulled out to the outside of the active area, and areelectrically connected with the electric supply portion formed on thearray substrate AR, respectively. Thereby, electric power of commonpotential is supplied to the first main common electrode CA1. That is,the first main common electrode CA1 and the second main common electrodeCA2 are electrically connected each other.

In case, the first main common electrodes CAL1 and CAL2 respectivelycover the source line S1 and the source line S2 in the active area, thewidth of the respective first main common electrodes CAL1 and CAL2 alongthe second direction X is substantially equal to or more than those ofthe source line S1 and the source line S2.

The pixel electrode PE is arranged between the source line S1 and thesource line S2 (i.e., between the first main common electrode CAL1 andfirst main common electrode CAR1). The pixel electrode PE has thebelt-like main pixel electrode PA linearly extending along the firstdirection Y and the belt-like capacitance portion PC linearly extendingalong the second direction X. In the illustrated example, the main pixelelectrode PA and the capacitance portion PC are formed integrally andcontinuously.

The main pixel electrode PA is arranged in an inside position of thepixel PX rather than the position on the adjoining source line S1 andthe source line S2, and is arranged between the source line S1 and thesource line S2. More specifically, the main pixel electrode PA isarranged in the approximately center position between the source line S1and the source line S2. In other words, the main pixel electrode PA isarranged in the approximately center position between the first maincommon electrode CAL1 and the first main common electrode CAR1. The mainpixel electrode PA extends from a vicinity of the upper portion end to avicinity of the bottom end portion of the pixel PX.

The capacitance portion PC is arranged at the upper portion end of thepixel PX, and is connected with one end portion of the main pixelelectrode PA. The capacitance portion PC linearly extends towardboth-sides of the main pixel electrode PA, i.e., the source line S1 andthe source line S2, or the first main common electrode CAL1 and thefirst main common electrode CAR1, respectively.

The capacitance portion PC faces the auxiliary capacitance line C1. Inthe illustrated example, the capacitance portion PC is arranged on theauxiliary capacitance line C1. Between the capacitance portion PC andthe auxiliary capacitance line C1, a first interlayer insulating film 12and a second interlayer insulating film 13 are interposed as insulatingfilms. However, when the pixel electrode PE is formed on the secondinterlayer insulating film 13 with the first main common electrode CA1,the capacitance portion PC is arranged so that the capacitance portionPC does not contact with the first main common electrode CAL1 and thefirst main common electrode CAR1 or are apart from the first main commonelectrode CAL1 and the first main common electrode CAR1. When the pixelelectrode PE is formed on a different layer from the first main commonelectrode CA1 through an interlayer insulating film which is notillustrated, the capacitance portion PC may be arranged so that thecapacitance portion PC intersects the first main common electrode CAL1and the first main common electrode CAR1 through the interlayerinsulating film which is not illustrated.

In addition, the gate line G1 may be arranged at the upper end portionof the pixel PX, and the auxiliary capacitance line C1 may be arrangedin the central portion of the pixel PX. In this case, the capacitanceportion PC is arranged in the central portion of the pixel PX, andcounters with the auxiliary capacitance line C1.

FIG. 7 is a cross-sectional view of the pixel of the liquid crystaldisplay panel LPN schematically showing a structure taken along line A-Ain FIG. 6. In this embodiment, a case is shown in which the first maincommon electrode CAL1 and the first main common electrode CAR1 arearranged on the second interlayer insulating film 13 with the pixelelectrode PE, and only the structure required for explanation isillustrated here.

The first main common electrode CAL1 and the first main common electrodeCAR1 are arranged at the both sides which sandwiches the main pixelelectrode PA. In other word, the main pixel electrode PA is arrangedbetween the first main common electrode CAL1 and the first main commonelectrode CAR1. The first main common electrode CAL1 counters with thesource line S1. The first main common electrode CAR1 counters with thesource line S2. Between the first main common electrode CAL1 and thesource line S1 and between the first main common electrode CAR1 and thesource line S2, the second interlayer insulating film 13 is interposedin the illustrated example, respectively. The pixel electrode PE, thefirst main common electrode CAL1 and the first main common electrodeCAR1 are covered with the first alignment film AL1.

The second main common electrode CAL2 and the second main commonelectrode CAR2 are arranged at the both sides sandwiching the positionright above the main pixel electrode PA. In other word, the main pixelelectrode PA is arranged between the second main common electrode CAL2and the second main common electrode CAR2. The second main commonelectrode CAL2 faces the first main common electrode CAL1. The secondmain common electrode CAR2 faces the first main common electrode CAR1.The second main common electrode CAL2 and the second main commonelectrode CAR2 are electrically connected with the first main commonelectrode CAL1 and the first main common electrode CAR1. The second maincommon electrode CAL2 and the second main common electrode CAR2 arecovered with the second alignment film AL2.

As above-mentioned, the first main common electrode CA1 and the secondmain common electrode CA2 overlap through the liquid crystal layer LQeach other, and the first main common electrode CA1 and the source lineS overlap through the insulating film each other. That is, the firstmain common electrode CA1, the second main common electrode CA2, and thesource line S are arranged on the same line.

The distance in the second direction X between the main pixel electrodePA and the source line S1, the first main common electrode CAL1 or thesecond main common electrode CAL2, is approximately the same as thatbetween the main pixel electrode PA and the source line S2, the firstmain common electrode CAR1 or the second main common electrode CAR2.

In the above structure, when displaying black image on the pixel PX,potential difference, i.e., electric field is not formed between thepixel electrode PE including the main pixel electrode PA and the firstmain common electrode CA1 and the second main common electrode CA2. Onthe other hand, when displaying white image on the pixel PX, electricfield is formed by the potential difference between the pixel electrodePE including the main pixel electrode PA and the first main commonelectrode CA1 and the second main common electrode CA2.

As illustrated, since the first main common electrode CA1 counters withthe source line, even if any one of the black image and the white imageis displayed on the pixel PX, it becomes possible to shield undesirableelectric field from the source line by the first main common electrodeCA1. The shield performance against electric field from the source lineis improved with the increase of the width of the first main commonelectrode CA1. However, since the aperture which mainly contributes tothe display is formed between the first main common electrode CA1 andthe main pixel electrode PA, if the width of the first main commonelectrode CA1 is too wide, the area of the aperture becomes small andreduction of transmissivity is caused.

Therefore, it becomes possible to raise the electric field shieldperformance by the electric field from the source lines whilemaintaining high transmissivity in the case where the first main commonelectrode CAL1 and the first main common electrode CAR1 are respectivelyarranged on the source line S1 and the source line S2, and havesubstantially the same width as the source line S1 and the source lineS2, respectively.

According to this embodiment, it is possible to suppress the applicationof undesirable bias from the source line to the liquid crystal layer LQby shielding undesirable electric field from the source line. Therebythe generation of cross talk is controlled. In other word, when thepixel potential which displays white is supplied to the source lineconnected to the pixel PX, the phenomenon of rising up of luminosityresulted from the generation of the disorder of the alignment of theliquid crystal molecule is suppressed in the state where the pixel PX isset to a potential to display the black image. Thereby, it becomespossible to control the generating of a poor display. Accordingly, ahigher quality liquid crystal display device can be offered.

According to this embodiment, the second main common electrode CAL2 andthe second main common electrode CAR2 face the first main commonelectrode CAL1 and the first main common electrode CAR1, respectively.When the first main common electrode CA1 and the second main commonelectrode CA2 are especially arranged right above source lines,respectively, the aperture is made large as compared with the case wherethe first main common electrode CA1 and the second main common electrodeCA2 are arranged on the main pixel electrode PA side rather than rightabove respective source lines, and it becomes possible to raise thetransmissivity of the pixel PX.

Moreover, it becomes possible to expand the distance between the mainpixel electrode PA and the second main common electrode CA2 or betweenthe main pixel electrode PA and the second main common electrode CA1 byarranging each of the first main common electrodes CA1 right above thesource line, and arranging each of the second main common electrodes CA2right above the first main common electrode CA1, and becomes possible toform more horizontal electric field closer to the horizontal direction.For this reason, it also becomes possible to maintain the wide viewingangle which is an advantage of the common IPS mode.

Moreover, it becomes possible to suppress the generation of undesiredvertical electric field, i.e., an electric field along the normal linewith respect to the substrate surface in a region where the first maincommon electrode CA1 and the second main common electrode CA2 face eachother sandwiching the liquid crystal layer.

Next, the effect of this embodiment is verified. FIG. 8A and FIG. 8B arefigures for explaining the definition of a cross talk rate introduced inthis embodiment.

As a first example, the luminosity was measured using a pattern in whicha window WDW is formed in approximately center portion of the activearea ACT as shown in FIG. 8A. The luminosities of four spots located infour directions adjacent to the window WDW are measured. Here, whileblack image and white image are displayed in the window WDW, theperipheral region displays the gray color image. The respectiveluminosities of four spots shown in the figure are denoted by W1, W2,W3, and W4. Next, as shown in FIG. 8B, the luminosities of the same fourspots as those shown in FIG. 8A were measured when same gray color imagewas displayed in the whole active area. The respective luminosities ofthe four spots are denoted as G1, G2, G3, and G4. In this case, thecross talk rate is defined as follows.

Cross talk rate=|W(n)−G(n)|/G(n)×100 (here, n=1-4)

First, the cross talk rate was measured about the same structure as thatof this embodiment except that the first main common electrode facingthe source line is not formed as a comparative example. Next, thestructure in which 60% of the source line width is covered with thefirst main common electrode, i.e., the covered rate of source line is60% is used as a first example according to this embodiment. Further,the structure in which 100% of the source line width is covered with thefirst main common electrode, i.e., the covered rate of source line is100% is used as a second example according to this embodiment.

When the cross talk rate of the comparative example is standardized as1, the cross-talk rate of the first example was 0.84, and the cross talkrate of the second embodiment was 0.49. Thus, in the case of the firstexample and the second example according to this embodiment, it wasverified that it is possible to reduce the generation of the cross-talk.

As explained above, according to this embodiment, it becomes possible tooffer a high quality liquid crystal display device.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. In practice, the structural and method elementscan be modified without departing from the spirit of the invention.Various embodiments can be made by properly combining the structural andmethod elements disclosed in the embodiments. For example, somestructural and method elements may be omitted from all the structuraland method elements disclosed in the embodiments. Furthermore, thestructural and method elements in different embodiments may properly becombined. The accompanying claims and their equivalents are intended tocover such forms or modifications as would fall with the scope of theinventions.

1. A liquid crystal display device, comprising: a first substrate including a first source line and a second source line extending in a first direction, a main pixel electrode arranged between the first source line and the second source line and extending in the first direction, and a pair of first main common electrodes arranged on the first source line and the second source line interposing an insulating layer and extending in the first direction, respectively; a second substrate including a pair of second main common electrodes arranged above the first main common electrode and extending in the first direction, the first main common electrode being connected with the second main common electrode; and a liquid crystal layer containing liquid crystal molecules and held between the first substrate and the second substrate.
 2. The liquid crystal display device according to claim 1, wherein the pair of the first main common electrodes are arranged on the first source line and the second source line, respectively, and having a substantially same width as those of the first and second source lines.
 3. The liquid crystal display device according to claim 1, wherein the main pixel electrode is formed on the insulating layer and formed of the same material as those of the couple of the first main common electrodes.
 4. The liquid crystal display device according to claim 1, wherein the distance between the first source line and the main pixel electrode in a second direction crossing orthogonally the first direction is substantially the same as that between the second source line and the main pixel electrode.
 5. The liquid crystal display device according to claim 1, wherein an initial alignment direction of the liquid crystal molecules is a direction in parallel to the first direction or an oblique direction crossing the first direction in a state where an electric field is not formed between the main pixel electrode and the first main common electrode, and between the main pixel electrode and the second main common electrode.
 6. The liquid crystal display device according to claim 1, further comprising a first alignment film covering the main pixel electrode and the first main common electrode formed on the first substrate, and a second alignment film covering the second main common electrode formed on the second substrate, wherein a first alignment treatment direction of the first alignment film to align initially the liquid crystal molecules and a second alignment treatment direction of the second alignment film to align initially the liquid crystal molecules are directions in parallel to the first direction or an oblique direction crossing the first direction.
 7. A liquid crystal display device having a plurality of pixels, comprising: a first substrate including; a first source line and a second source line extending in a first direction, a main pixel electrode arranged between the first source line and the second source line and extending in the first direction, a pair of first main common electrodes arranged on the first source line and the second source line interposing an insulating layer therebetween and extending in the first direction, respectively, a gate line formed extending in a second direction orthogonally crossing the first direction and crossing the pixel, a pair of capacitance lines formed at an upper side end portion and a lower side end portion of the pixel extending in the second direction, and a capacitance portion located at one end of the main pixel electrode and facing one of the capacitance lines, a second substrate including a pair of second main common electrodes arranged above the first main common electrode and extending in the first direction, the first main common electrode being connected with the second main common electrode; and a liquid crystal layer containing liquid crystal molecules and held between the first substrate and the second substrate.
 8. The liquid crystal display device according to claim 7, wherein the gate line is arranged approximately in the central portion of the pixel.
 9. The liquid crystal display device according to claim 7, wherein the first source line, the first main common electrode, and the second main common electrode are aligned on a same normal line with respect to the surface of the first and second substrates.
 10. The liquid crystal display device according to claim 7, wherein the pair of the first main common electrodes are arranged on the first source line and the second source line, respectively, and having a substantially same width as those of the first and second source lines.
 11. The liquid crystal display device according to claim 7, wherein the main pixel electrode is formed on the insulating layer and formed of the same material as those of the couple of the main common electrodes.
 12. The liquid crystal display device according to claim 7, wherein the distance between the first source line and the main pixel electrode in the second direction is substantially the same as that between the main pixel electrode and the second source line.
 13. The liquid crystal display device according to claim 7, wherein an initial alignment direction of the liquid crystal molecules is a direction in parallel to the first direction or an oblique direction crossing the first direction in a state where an electric field is not formed between the main pixel electrode and the first main common electrode, and between the main pixel electrode and the second main common electrode.
 14. The liquid crystal display device according to claim 7, further comprising a first alignment film covering the main pixel electrode and the first main common electrode formed on the first substrate, and a second alignment film covering the second main common electrode formed on the second substrate, wherein a first alignment treatment direction of the first alignment film to align initially the liquid crystal molecules and a second alignment treatment direction of the second alignment film to align initially the liquid crystal molecules are directions in parallel to the first direction or an oblique direction crossing the first direction.
 15. A liquid crystal display device having a plurality of pixels, comprising: a first substrate including; a first source line and a second source line extending in a first direction, a main pixel electrode arranged between the first source line and the second source line and extending in the first direction, a pair of first main common electrodes arranged on the first source line and the second source line interposing an insulating layer therebetween and extending in the first direction, respectively, a gate line formed extending in a second direction orthogonally crossing the first direction and crossing the pixel, a pair of capacitance lines formed at an upper side end portion and a lower side end portion of the pixel extending in the second direction, and a capacitance portion located at one end of the main pixel electrode and facing one of the capacitance lines, a second substrate including a pair of second main common electrodes arranged above the first main common electrode and extending in the first direction, the first main common electrode being connected with the second main common electrode; and a liquid crystal layer containing liquid crystal molecules and held between the first substrate and the second substrate; wherein the distance between the first source line and the main pixel electrode in the second direction is substantially the same as that between the main pixel electrode and the second source line, and wherein the initial alignment direction of the liquid crystal molecules is a direction in parallel to the first direction or an oblique direction crossing the first direction in a state where an electric field is not formed between the main pixel electrode and the first main common electrode, and between the main pixel electrode and the second main common electrode.
 16. The liquid crystal display device according to claim 15, further comprising a first alignment film covering the main pixel electrode and the first main common electrode formed on the first substrate, and a second alignment film covering the second main common electrode formed on the second substrate, wherein a first alignment treatment direction of the first alignment film to align initially the liquid crystal molecules and a second alignment treatment direction of the second alignment film to align initially the liquid crystal molecules are directions in parallel to the first direction or an oblique direction crossing the first direction.
 17. The liquid crystal display device according to claim 15, wherein the first source line, the first main common electrode, and the second main common electrode are aligned on a same normal line with respect to the surface of the first and second substrates. 